Method and device for shaping an orthodontic archwire

ABSTRACT

An apparatus for bending orthodontic wires has means for guiding and holding a wire. In order to prevent forces resulting from compressive or stretching strain during the bending process, one of these means does not apply any longitudinal forces onto the wire by design. In another implementation, the apparatus for bending orthodontic wires has a gimbal-mounted gripper for bending the wire. Furthermore, a method is disclosed for applying two bends at the same longitudinal wire location in two different directions.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISK APPENDIX

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BACKGROUND OF THE INVENTION

The present invention relates to methods for applying a desired shape toarchwires to be used in orthodontic appliances for the straightening ofteeth, and more particularly, to the automated manufacture of customizedarchwires using robotic devices.

The common approach for orthodontic appliances is to bond small metallicparts (“brackets”) onto the outer (“labial”) side of the teeth, and toinsert a wire into the slots of the brackets. The wires are typicallypreformed off-the-shelf wires, and the brackets are bonded basing onvisual judgment by the orthodontist. However, the use of computerizedprocesses in orthodontics increases. Especially when the brackets arebonded to the back side of the teeth (“lingual orthodontics”), the useof computer assisted processes for designing the brackets andmanufacturing the wires has achieved a significant market share. Usingcomputerized processes typically results in providing a numericdescription of an orthodontic archwire.

Devices for bending orthodontic archwires have been proposed in theprior art. In U.S. Pat. No. 5,431,562, Andreiko et al. describes anapparatus that takes a straight archwire and imparts a simple planararcuate curvature to the wire. However, the Andreiko et al. wire bendingapparatus cannot produce any complex and twists bends in the wire, e.g.,bends requiring a combination of translation and rotational motion.

In U.S. Pat. No. 6,612,143 (“Robot and method for bending orthodonticarchwires and other medical devices”), Butscher et al. discloses a robotcapable of bending fully three-dimensional orthodontic archwires. Thedevice comprises two grippers, one of the grippers being mounted to asix-axis-robot arm and thus moveable. The gripping tools preferablyincorporate force sensors which are used to determine overbends neededto get the desired final shape of the archwire. The manufacturingprocess uses straight pieces of wire and step by step applies bendsand/or twists to the wire, thus forming an archwire. The process asdescribed in the '143 patent requires the calculation of the consumedwire length for a bend. Even a slight miscalculation of the consumedwire length for a bend generates significant forces along thelongitudinal axis of the wire. Those high forces arising by estimatingan improper consumed wire length for a bend will superimpose the bendingforces and significantly disturb the desired measurements of thoseforces.

The patent to Orthuber et al., U.S. Pat. No. 4,656,860 also describes abending robot for bending archwires. A robot as described in the '860patent was manufactured and sold as part of a complete orthodonticsolution by Geyer Medizintechnik GmbH in Berlin, Germany, but neverwidely commercialized. The robot consisted of two characteristic designfeatures: a bending cone that could move forwards and backwards to bendthe wire, and a rotating cone that could twist the wire. As such, itcould only apply torque or bends over the two main axes of a crosssection of a rectangular shaped wire. Basing on the embodimentdistributed by Geyer Medizintechnik GmbH, a series of three twists andtwo bends were required to shape an archwire so that it would fit in theslots of two adjacent brackets. This series of twists and bends requiredas much as 5 mm of wire length between adjacent brackets. This length ofwire is greater than that available for closely spaced teeth, especiallyin lingual orthodontics.

The present invention presents substantial improvements over prior artas disclosed in the cited applications.

BRIEF SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide a reliableand efficient method for applying a permanent customized shape to anorthodontic archwire using robotic devices.

If a device similar to the description in U.S. Pat. No. 6,612,143 isused, it is preferable over the disclosed apparatus to replace one ofthe grippers with a bushing for supporting and guiding the wire. Such aguide bushing would preferably be adapted to the cross section of thewire in order to allow for precise twists. The design of the bushingwould be optimized for low friction. In a preferred embodiment, thebushing is mounted to the base plate of the robot. The moveable armcarries the gripper as described in the '143 patent. The wire would befed through the bushing. The moveable gripper would grip the wireextending through the bushing and pull a predefined length of the wireout of the bushing, said length basing for instance on best estimates asdisclosed in the '143 patent. During the bending process, thediscrepancy between the calculated and the actual consumed wire lengthfor the bend would generate longitudinal forces. These forces wouldcause the wire to slip through the bushing and therefore automaticallycorrect the discrepancy. Only the amount of friction forces between thewire and the bushing would remain, and these forces can be minimized bya variety of means.

In another embodiment, a device as disclosed in U.S. Pat. No. 4,656,860is used. As implemented by Geyer Medizintechnik GmbH, Berlin, Germany,specific straight portions of the wire are assigned to specific bracketslots. The original implementation of the robot used a sequence of threetwists and two bends in order to define a geometry leading from astraight wire portion assigned to a first slot to a straight wireportion assigned to a second slot. While this implementation hasspecific advantages, it has the big disadvantage of consumingsignificant wire length. Due to the design of the robot, after eachtwist action a relevant wire feed is required before the next bend maybe applied. Therefore the required total wire length from the end of onebracket slot to the beginning of a second bracket slot quickly adds upto approx. 5 mm, depending on the specific amounts of bends and twistsand the specific mechanical layout of the robot. For lingual archwires,this is far too much. Especially the lower front teeth often have awidth not exceeding 5 mm, and the arch length of a lingual wire is evenshorter that the length of the dental arch. Additionally, a bracketwidth of 2 mm minimum can be assumed, so that the available lengthbetween two brackets is below 3 mm.

In order to overcome this limitation, an alternative command sequence isgenerated. Instead of applying a twist followed by a bend, two bends atthe same location along the wire axis, but in different directions areapplied. This has the same effect like the original sequence, butconsumes much less wire length. Only one twist between the couple ofbends has to be applied in order to adapt the rotational orientation ofthe wire.

In yet another embodiment of the invention, a modified device is used.Both devices disclosed in the '143 and in the '860 patent haveweaknesses in ensuring the desired precision of the applied bends andtwists. The device according to the '860 patent clamps the wire onlybelow the point where it is bent. The portion of the wire extendingbeyond the cone is free and unconstrained; the robot had no control asto the effective deformation of the wire. Therefore, the materialproperties of the wires to be used have to be calibrated in a tediousprocess, and very tight material tolerances have to be maintained. Thedevice according to the '143 patent does clamp the wire on both ends ofthe applied deformation. However, in order to control the precise shapeof the bent wire, the residual spring-back forces are measured. This isa process prone to errors, especially since side effects as discussedbefore will introduce additional disturbances.

The device according to this invention clamps the wire on both ends ofthe portion to be deformed. Unlike the device disclosed in the '143patent, it has restricted capabilities with respect to the shapes thatmay be applied to the wire, but it can be build using a mechanicallyextraordinarily stiff design. This stiff design is the foundation forthe principle of measuring the precision of the applied deformations.After applying the force for the deformation, one of the grippers isdecoupled from any driving force, but remains clamped to the wire. Now,the exact location and orientation of the gripper is measured, directlyreflecting the new shape of the wire. Depending on the predefinedtolerances, the deformation may be refined by subsequent application ofcorrective forces, or the deformation is accepted. Due to the stiffdesign, a combination of bends and twists can be applied at onelocation. Unlike the device disclosed in the '860 patent, the devicedisclosed in this application it is not limited to bends along a mainaxis of the cross section.

The device comprises mainly a guide bushing for guiding the wire on oneside of the deformation to be applied and a gripper for clamping thewire on the opposite side of the deformation to be applied. While theguide bushing is fixed, the gripper is mounted on three bearings. Thefirst bearing allows rotating the gripper around the longitudinal axisof the wire in order to apply the twisting component of the deformation.The second bearing is mounted around the gripper and the first bearingand allows to apply the bending component to the deformation. The thirdbearing is mounted around the second bearing and allows to adjust thedirection of bending. The gripper is therefore gimbaled. The gripper isalso completely balanced around its centers of motion. All threebearings are designed to cause very low friction, and three axes areequipped with contact-free rotary encoders. If the gripper clamps ontothe wire, and no external force is applied to the gripper, therotational angles of the three axes (provided by the rotary encoders)will precisely document the passive or relaxed shape of the wire. If thepresent shape is not within the tolerances of the nominal shape,corrective movements are to be made by the gripper. These movements canbe initiated manually or by actuators. If actuators are used, and thesignals of the rotational encoders are processed accordingly, theprocess shaping the wire could be fully automated, provided thatadditional means for feeding the wire are present and that the clampingfunctionality of the gripper is also actuated. In a preferredembodiment, the actuators can be coupled to the axes and fully decoupledwhile the measurement of the actual wire shape is performed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 illustrates a straight piece of wire being held by two grippers.The calculated consumed wire length for the bend is indicated in thecenter of the wire and equals the distance between the end of the firstgripper and the beginning of the second gripper.

FIG. 2 illustrates how a wire is bulged if the actual consumed wirelength for the bend is shorter that the calculated length represented bythe original distance between the two grippers.

FIG. 3 illustrates a straight piece of wire being held by a bushing anda gripper. The calculated consumed wire length for the bend is indicatedin the center of the wire and equals the distance between the end of thebushing and the beginning of the gripper.

FIG. 4 illustrates that the wire has slipped through the bushing, andthis wire motion has relaxed the bended portion. There is a noticeabledifference between the originally calculated consumed wire length forthe bend, indicated by the line in the center of the wire, and theactually consumed wire length.

FIG. 5 is a perspective view of a piece of wire that has been bentaround two axes at mainly the same wire position.

FIG. 6 is a perspective view of a wire segment that has been bentaccording to the classic algorithm, having two bends and three twists.

FIG. 7 is a perspective view of a wire segment that has been bentaccording to the method disclosed in this application, having four bendsand one twist.

FIG. 8A is a view onto a wire that has already been bent in onedirection. The end points of the line of impact for application of thesecond bend are located on both sides of the midline.

FIG. 8B is a side view onto a wire that has already been bent andillustrates the bending finger contacting the wire for the second bend.

FIG. 9 is a view onto a wire that has already been bent in onedirection. Both end points of the line of impact for application of thesecond bend are located on one side of the midline.

FIG. 10 is a perspective view of a group of wire segments that areconnecting two slot segments according to the method disclosed in thisapplication, having four bends and one twist.

FIG. 11 is a flow diagram of calculating the required bends and twistsaccording to the method disclosed in this application.

FIG. 12 displays an iterative optimization of two angles in a simplifiedmanner.

FIG. 13 is a cross-sectional view of a device for shaping orthodonticwires.

FIG. 14 is a cross-sectional top view of the device of FIG. 13, seenfrom view line A in FIG. 13.

FIG. 15 displays an alternate layout of the device of FIG. 13.

FIG. 16 displays a portion of a wire having a bend deviating from thedesired angle.

FIG. 17 displays the wire of FIG. 16 with a second bend, the second bendcompensating the deviation of the first bend.

DETAILED DESCRIPTION OF THE INVENTION

Six Axis Robot Having One Gripper

The robot as disclosed in U.S. Pat. No. 6,612,143 comprises twogrippers, one of the grippers being mounted to a six-axis-robot arm andthus moveable in all six degrees of freedom. The other gripper is fixedto the base plate of the robot. The gripping tools preferablyincorporate force sensors which are used to determine overbends neededto get the desired final shape of the archwire. The manufacturingprocess uses straight pieces of wire and step by step applies bendsand/or twists to the wire, thus forming an archwire. The process asdescribed in the '143 patent requires the calculation of the consumedwire length for a bend. In column 16 line 64 ff. it is described howsuch a calculation can be performed. Also, FIG. 20B displays a proposedalgorithm. From the specification it becomes obvious that the exactcalculation of the required straight wire length is not possible. Even aslight miscalculation of the consumed wire length for a bend generatessignificant forces along the longitudinal axis of the wire, since a wireas used for orthodontics purposes may be flexible in the directiontransversal to its longitudinal axis, but is extremely stiff in thelongitudinal axis. Depending on the veracity of the calculations, theforces generated by estimating an improper consumed wire length for abend can significantly exceed the forces actually required for bendingthe wire. This is a very undesired side effect since the whole conceptof the '143 patent bases on the precise measurement of forces generatedby bending the wire. The high forces arising by estimating an improperconsumed wire length for a bend will superimpose the bending forces andsignificantly disturb the desired measurements of those forces.

The term “bend” as used in this specification and the claims can mean apure bend, a pure twist or a combination of both. This is in line withthe general usage of the term “bend” in orthodontics. A pure twist isreferred to as a “3rd order bend” by orthodontists.

Patent '143 describes in great detail the usage of force sensors inorder to determine the required overbending of the wire. From thespecification it becomes obvious that the proposed process is not veryfault tolerant. It can easily be imagined that various influences likelongitudinal forces as described above or the mechanical flexibility ofan off-the-shelf six-axis-robot will be highly disturbing and may evencorrupt proper function.

The calculated length consumed for a bend reflects the distance betweenthe two grippers before the bending process starts, in other words whilethe wire is still straight.

An exact calculation of the straight wire length consumed for a bend hasnot yet been introduced. The reason is that if a significant amount ofbending forces is applied to a wire, not only bending but also shearingdeformations will occur, and accordingly the cross section of the wirewill change. Only slightest changes in the cross section can have agreat effect on the exact location of the neutral axis. The neutral axisis the zone where no tensile forces and no compression forces areactive. Theoretically, the length of the neutral axis as a firstapproximation is equal to the consumed wire length. However, allcalculations and approximations do typically not exactly reflect thetrue outcome, and toolmakers will always run a couple of tests with thenominal material before they start designing a tool.

The disadvantage of performing a calculation is that due to thelongitudinal stiffness of a wire, even a slight miscalculation of theconsumed wire length leads to significant longitudinal forces. Forinstance, if the required wire length for a bend would be 3 mm, and thecalculation produces a result of 2.9 mm, an error of 0.1 mm wouldresult. The longitudinal force within a wire portion of stainless steelhaving a length of 3 mm and a cross section of 0.017″×0.025″ resultingfrom compression or elongation of 0.1 mm will be approx. 1700N. Thisexceeds by far the forces that are active in order to bend the wire. Thetrue forces may be lower because the wire will not actually becompressed but bulge, and the mechanical structures of the bending robotwill also have certain flexibility. It is obvious, however, that thebending process itself and all force measurements will be significantlysuperimposed and disturbed by the longitudinal forces.

The solution to this problem is to clamp the wire only on one side ofthe deformation zone. In a preferred embodiment, a gripper that ismounted to the arm of the six-axis-robot will clamp the wire and performthe bending and twisting movement. On the opposite side of thedeformation zone, a low friction guiding bushing will support the wirein order to maintain the integrity of the desired deformation, but willrestrict longitudinal movements as little as possible. The calculationsof the consumed wire length for a bend can be executed as taught in the'143 patent. However, while the bending and twisting process isperformed, the wire can slip through the bushing in order to compensatefor any error in the calculation.

FIG. 1 shows a straight piece of wire 1 held by a fixed gripper 18 and amoveable gripper 4. Line 3 illustrates the calculated wire length thatwill be consumed for the bend according to the calculations. FIG. 2illustrates the result of the deformation if the calculated consumedwire length is longer than the actually consumed length. The wire willshow a bulge. The actual shape of the bulge depends widely on thedeformation, the cross section and material of the wire, the distancebetween the grippers and the flexibility of the 6-axis-robot.

FIG. 3 shows a straight piece of wire 1 supported by a bushing 2 and amoveable gripper 4. Line 3 illustrates the calculated wire length thatwill be consumed for the bend according to the calculations. FIG. 4illustrates the result of the deformation. The wire 1 has slippedthrough bushing 2. This movement compensates the discrepancy between thecalculated consumed wire length and the actually consumed length.Precise knowledge of the amount of the wire length that has slippedthrough the bushing is not required. For obtaining a precise wire shape,only the wire between the bushing and the gripper is relevant. The wireportion that has slipped will either add to the straight length ready tobe fed for the next bends and twists or will be subtracted from thatstraight length, depending of the mathematical sign of the discrepancy.As long as enough straight wire length remains to be fed through thebushing for consecutive bends, the exact amount of the remainingstraight wire length must not be known. Assuming that the calculationsare reasonably precise, the summarized overall discrepancy betweencalculated and actually consumed length will not exceed 5 mm, so it issufficient to provide a straight wire length at the beginning of thebending process showing this additional safety margin in length.

The design of the bushing must ensure low friction between the wire andits support. There are several options. One option is to have a bushingthat is coated with polytetrafluoroethylene or another plastic designedfor low friction bearings. Another option is to add oil to the contactsurface. In both cases, the slipping movement can be also supported bytemporarily applying vibrations to the bushing. This is a commonapproach in industrial automation when parts for instance are supposedto slide down a chute. If the parts tend to get stuck because the angleof the chute being to flat, a vibrating device is mounted to the chute.Another option is to use roller bearings. The four walls of the bushingcould be substituted by eight needles that would be located at the edgesof the bushing. Each needle would be pivoted by roller bearings. Also, acombination of roller bearings and plain bearings can be appropriate.

Alternative Implementation of Bending Robot According to Orthuber

Another implementation of the present invention uses a bending robot asdisclosed by Orthuber et al. in U.S. Pat. No. 4,656,860. A deviceaccording to the invention has been built and distributed as part oftheir “bending art system” by Geyer Medizintechnik GmbH in Berlin,Germany, in close cooperation with Dr. Orthuber. The “bending artsystem” came complete with software for designing the wire shape and forcontrolling the robot. The robot as disclosed in the '860 patentconsists of two characteristic design features: a bending finger (apartial cone) that can move forwards and backwards to bend the wire, anda rotating cone that can twist the wire. The wire is held during bothbending and twisting operations by the outer clamping cone.

Since the robot as disclosed by Orthuber et al. in the '860 patentproduces a wire consisting of straight portions, bent portions andtwisted portions, it is obvious to assign straight portions to bracketslots. In other word, a specific straight portion of the wire issupposed to be located within the slot of a specific brackets sloteither during treatment or at the end of treatment. The portions betweentwo adjacent slots can be used to apply twists and bends to the wire inorder to obtain a spatial shape dictated by the therapeutic task. Thespatial relationship between two adjacent slots will typically bedefined in mathematical terms in the numeric wire description.

The device has several restrictions. Bends and twists have to be appliedto separate locations along the wire. Also, the portion of the wireextending beyond the cone is free and unconstrained, and therefore onlybends over the two main axes of a cross section of a rectangular shapedwire can be applied. A bend in any direction other that one of the mainaxes would create side effects due to oblique bending.

Geyer Medizintechnik GmbH has solved this problem by introducing analgorithm comprising a series of three twists and two bends. FIG. 6shows an exemplary wire section. The wire section has two segments 8 and14 that are assigned to bracket slots.

The relative spatial location and orientation between these two segmentsis therefore given. A portion of an orthodontic wire being assigned to aslot is referred to as “slot segment” in this application. Segment 8 isaccordingly referred to as first slot segment and segment 14 second slotsegment. Also, the bend adjacent to the first slot segment is named“first” bend. This order has been selected arbitrarily and does notimply the order of manufacturing. Basically, both slot segments have tobe connected by a piece of wire. The first bend 10 can be understood asthe beginning of the connecting segment, while the second bend 12 is theend of the connecting segment. In order to adjust the direction of bend10 with respect to the orientation of the first bracket slot, a firsttwist 9 is required. Likewise, the third twist 13 adjusts the directionof bend 12 with respect to the orientation of the second bracket slot.Yet another twist 11 is required in order to compensate for thediscrepancy of the orientation of the main axes of both bends.

While this concept represents a universal approach, it has significantdisadvantages and limitations. Firstly, the distance between a bend anda twist is dictated by the design and the dimensions of the robot. Thedevices sold by Geyer Medizintechnik GmbH required a minimal distance of0.7 mm between a bend and a consecutive twist and a minimal distance of0.9 mm between a twist and a consecutive bend. It is easily understoodthat the series of twists and bends therefore required as much as 5 mmof wire length between adjacent brackets. This length of wire is greaterthan that available for closely spaced teeth, especially in lingualorthodontics.

Secondly, relevant twists are present in the wire simply to adjust thedesired direction of a bend. Depending on the individual geometry,twists up to 90° can be required for a rectangular wire. In order toconsume little wire length for twists, the devices sold by GeyerMedizintechnik GmbH show a distance between the twisting clamps of lessthan 0.3 mm. Even for ductile materials, a 90° twist applied to a wireportion shorter than the side length of the cross section is achallenge. Many materials used for orthodontic wires like shape memoryalloys or beta-titanium break instantaneously when exposed to suchstress.

This invention introduces a new method for bending and twisting a wireusing the device as disclosed in the '860 patent. Instead of applyingone bend and one twist in order to adjust the direction of the bend, twobends in the directions of the two main axes are applied. Sinceorthodontic archwires are typically smoothly curved, following the formof the jaw, only relatively small bends are required in most cases. Evenif individual adjustments are required in order to adapt a wire to amisplaced bracket or in order to re-adjust the treatment goal, therequired steps in the wire are typically below 1 mm. Therefore, it isoften possible to bend the wire in one direction, then turn it 90°around its longitudinal axis and apply a second bend at the sameposition. FIG. 5 shows a wire having two bends at one location. Thebending axis for bend 7 is the Y-axis. Bend 6 has been applied aroundthe Z-axis.

FIG. 7 shows the same slot segments 8 and 14 as in FIG. 6. However, bend10 and twist 9 of FIG. 6 are substituted by bends 6 and 7. Accordingly,bend 12 and twist 13 of FIG. 6 are substituted by bends 16 and 17.Similar to the method used in FIG. 6, a twist 15 is required between thebends in order to compensate for the discrepancy of the orientation ofthe main axes of the bends. By comparing FIGS. 6 and 7, the advantage ofthe proposed method is evident. The overall length of requireddeformations is much shorter, and the amount of deformations is reduced.Only one twist is required, having a much lower value than required bythe old method.

Placing two bends at one location is possible as long as the first bendis not too large. When the bending finger of the device according to the'860 patent touches the wire, the contacting forces are applied along aline. FIG. 8A shows a wire 42 that has already been bent in onedirection. Line 40 is the top edge of the outer clamping cone. Theportion of the wire 42 that is extending above the cone is to be bent inthe second direction. The contacting line of the bending finger has aspecified height 37 above the top edge of the outer clamping cone. Therobots delivered by Geyer Medizintechnik GmbH show a dimension of 0.9mm. Both endpoints 38 and 39 of the contacting line are located onopposite sides of the center line. FIG. 8B shows a side view of thesituation displayed in FIG. 8A. A forward movement of the bending finger41 will induce a proper bend.

FIG. 9 shows a wire 42 that has a first bend of a significantly higherangle. In this case, both endpoints of the contacting line are locatedon the same side of the center line. A forward movement of the bendingfinger will also induce a twisting movement onto the wire, since bothforce transmission points are placed asymmetrically on one side of thecenter line. The result will be an undefined mixture of bend and twist.To solve this problem, the order of the bends can be changed. If thesecond bend is smaller, it would be useful to apply that bend first andthen the other, larger bend.

In case both bends are too large, a feed motion of the wire is requiredbefore the second bend is applied. In other words, the second bend isplaced a short distance away from the first bend. This does obviouslyconsume some wire length, but is still more efficient than having atwist instead of the bend.

In order to determine the required commands for the bending robot, itwould be possible to use an analytic approach. Due to the variousconstraints and options regarding the order of bends, an iterativeapproach seems more adequate. FIG. 11 shows a flow chart of a preferredembodiment of method steps for calculating the command sequence for therobot. In order to obtain a good starting point for the iterativeoptimization, it is useful to execute step 20 and calculate four anglesas starting points by virtually connecting the two slot segments by aline and projecting the connecting line onto the main planes. If thiscalculation is not performed, this does not have any negative effect onthe end result, it just slows the calculation down by adding moreiterative steps. Step 21 is the beginning of an outer loop, and step 22is the beginning of an inner loop. In steps 23 to 26, the angles of thebends are gradually modified, together with the length of the straightwire segments (the process of gradually modifying and optimizing anangle is demonstrated in a simplified manner in FIG. 12). In step 27,the twist angle is obtained by calculating the angles between the edgesof the wire segments adjacent to the twist (see segments 33 and 34 inFIG. 10). Now the remaining error is determined. One option is tocalculate the normal vector for each surface terminating a segment (asshown in FIG. 12), and to determine the error in parallelism of bothterminating surfaces of each segment. If a predefined value is exceeded,a new iterative loop is executed. Otherwise, the iterative loop is left(step 28). In step 29, the constraints are checked. If a bending angleis too large so that both endpoints of the contacting line of thebending finger are located on the same side of the center line, anotherorder of bends is tested or, if all orders have been tested, thedistance between paired bends is increased (step 30). In each case, anew iterative process for re-calculating the angles is required.Finally, the result is exported as ASCII file. The robots sold by GeyerMedizintechnik GmbH are fed with files having a simple format. Each linehas a specific command type, indicated by a number (feed: 10; bend: 12;turn: 15; twist: 11), followed by one or more blanks and the value (witha maximum resolution of two digits after the decimal point).

FIG. 10 shows a perspective view of the straight segments of a wireportion extending from one slot segment 31 to the next slot segment 36.Segment 31 is followed by a bend, and the adjacent segment 32 providesthe necessary distance between the two bends (both bends are very largeand need to be separated from each other). Segment 32 is followed by thesecond bend and then by segment 33, which actually embodies one part ofthe connecting segment which virtually connects the slot segments.Adjacent segment 34 embodies the other part, both segments beingseparated respectively joined by the twist (that is displayed with alength of zero for a better understanding of the underlying geometry).Segment 34 is followed by the third bend and by another separatingsegment 35. The length of segment 35 is shorter because the thirdbending angle is much smaller than the first angle and requires lessfeed until the endpoints of the contact line of the bending finger arelocated on both sides of the center line. Segment 35 is followed by thefourth bend and is adjacent to slot segment 36.

FIG. 12 displays in a simplified manner the iterative process ofoptimizing angles. In this drawing, only two angles are to be optimized.Step I shows the initial situation. In step II, the first angle isoptimized in a resolution of 5° in a manner that the normal vector onthe angled surface passes the center of the opposite angled surface asclose as possible. The result in this example is 45°. In step III, theopposite surface is optimized in the same manner, ending up with 20°. Infurther loops, the angles are iteratively optimized one by one, whilethe resolution is increased. After performing step IX, the first bendhas 46.48° and the second bend 17.26°. The length L of the virtualconnecting segment can also easily be calculated basing on the spatialarrangement of the two segments to be connected.

Apparatus for Bending Orthodontic Wires

In yet another implementation of the invention, an optimized apparatusis used. It has been explained earlier that the apparatus disclosed inU.S. Pat. No. 6,612,143 has the advantage of shaping the wire portionbetween two slot segments in one section, but the verification of theaccuracy of the deformation requires significant efforts and is prone toerrors. The device disclosed in U.S. Pat. No. 4,656,860 is stiff androbust, but requires up to five independent deformations to be appliedone after another and has no means for a verification of the accuracy ofthe deformation, thus requires the use of calibrated wire materials.

This application presents a device that allows shaping a wire byapplying two deformations in order to connect to slot segments. Eachdeformation consists of a combined bend and twist. This is achieved byclamping the wire with one moveable gripper and a fixed gripper or afixed guiding bushing. The moveable gripper is gimbal-mounted and hasthree degrees of freedom. This limits the scope of deformations, butallows for a robust and stiff design of the apparatus. The stiff designis a valuable precondition for verification of the applied deformation.In a preferred embodiment, the device measures directly the resultingdeformation by decoupling the gripper from any external forces andmeasuring the angles of the three axes with the wire dictating thespatial orientation of the gimbal axes.

FIG. 13 shows a preferred embodiment of the invention. A wire feedingmechanism 58 is mounted to a base plate 55. A plurality of options isapplicable. Friction rollers can be used as well as a mechanism whichclamps the wire and moves in incremental steps. The feeding mechanismcan be activated for instance by steppers or servo motors. In additionto feeding the wire, the wire feeding mechanism 58 should alsomechanically guide the wire at its outlet. This is to ensure that thedeformation zone of the wire is well defined and limited to the portionof the wire extending from the feed mechanism. One option to support andguide the wire would be a clamping mechanism that clamps the wire afterthe feeding movement is finished. Another option is a low frictionbushing. This second option is favorable in light of the problemsarising when the consumed length has been calculated imprecisely, andhigh longitudinal forces develop.

The first axis of the gimbal-mount could be named “rotational axis”. Theterm “axis”, as used in the specification and the claims, when directedto an apparatus, shall mean a configuration of means of the apparatusallowing a directed movement of portions of such means; including butnot limited to rotational and translational movements.

The first axis or rotational axis is realized by ball bearing 56. Therotational base 51 can accordingly rotate around this axis, which is inline with the longitudinal wire axis of the undeformed wire inside thefeeding mechanism. Rotational base 51 carries ball bearings 52,embodying the second gimbal axis that could be named “bending axis”. Therotational base 51 carries also the encoding disk 64 of rotary encoder50. Ball bearings 52 carry the bending base 59 which accordingly rotatesaround the bending axis. Bending base 59 holds ball bearing 63 whichincorporates the third gimbal axis, the “twist axis”. The names for theaxes have been selected in order to improve descriptiveness. The bendingbase 59 carries also the encoding disk 53 of rotary encoder 54. Ballbearing 63—incorporating the twist axis—holds twist base 60. Twist base60 carries the encoding disk 62 of rotary encoder 57. It also holdsgripper unit 61. Gripper unit 61 has the task of clamping the wire withgripper fingers 66 during the deformation process and, if applicable,also during the verification process.

Again, a wide variety of design principles is applicable. Possibleimplementations for actuating the gripper fingers include, but are notlimited to solenoids, pressurized air and electric motors.

FIG. 14 shows the apparatus in a cross-sectional top view. The line ofview is indicated in FIG. 13 by arrows A. Deviating from FIG. 13,bending base 59 is tilted around the bending axis. Also, a wire 65 thatis currently being bent is displayed. The deformation is applied to thewire zone between feeding mechanism 58 and gripper fingers 66. After thedeformation is applied and, if applicable, verified, the gripper unit isreleased, all three gimbal axes are reset to zero, and the wire is movedforward in order to apply deformations to the next wire section.

A preferred method of operating the device is to obtain a numeric wiredescription similar to the one that was used by Geyer MedizintechnikGmbH to operate the robot of the '860 patent. The appropriate bends andtwists that need to be applied to the wire can be calculated asdescribed above. The main advantage of the new design is that the twobends that are placed in close proximity or at the same location can nowbe substituted by one bend. Since the wire is restrained on both sidesof the deformation zone, an oblique bend, that is a bend where thebending axis is not identical to one of the main axes of the crosssection, can be applied. The direction of the bend can be adjusted byrotating rotational base 51 to the correct position. As explained inFIGS. 7 and 10, an additional twist is typically required between twoslot segments. This twist can be applied to the wire by rotating thegripper unit 61 around the twist axis. The twisting deformation isapplied to the same zone as the bending deformation. With respect to theamount of torque, it is possible to apply the complete twisting angle toone deformation, but the twist can also be distributed over bothdeformation zones that are located between two slot segments.Temporally, the twisting deformation can be applied before the bend,simultaneously or after the bend.

The forces for bending and twisting the wire can be applied manually byan operator, or by using actuators. Applicable actuators include, butare not limited to steppers and servo motors. In a preferredenvironment, also the feeding mechanism 58 is controlled by a computer,so that the process of bending and twisting the wire can be fullyautomated.

The device as disclosed has several significant advantages. The designis simple and can be realized by using mainly inexpensive off-the-shelfcomponents. Since only two deformations are required to shape the wirebetween two slot segments, the operation is much faster compared to theoperation of the device of the '860 patent, where five deformingoperations and several feed operations are required. Due to its stiffdesign and the option to have completely balanced axes with very lowfriction, a very reliable feedback loop for verification of the truewire shape as described below can be easily integrated.

FIG. 15 shows an alternate layout of the apparatus. Here, the bendingaxis is attached directly to base plate 55. The rotational axis isrealized by mounting wire feeding mechanism 58 to bearings 56. In thisway, the relative rotational movements between bending base 59 and wirefeeding mechanism 58 are enabled in the same manner as in FIG. 13. Theadvantage of this layout is that gripper unit 61 has only two degrees offreedom with respect to the base plate. This eases routing theumbilicals for energy supply and sensor signals.

Method for Verifying the Actually Bent Shape of an Orthodontic Wire

The method disclosed in this application requires an apparatus having atleast two tools that can either grip the wire or at least partiallyembrace the wire in order to fully adapt to the spatial position of aportion of the wire at two different locations. The term “position” asused in this specification and the claims shall mean either a locationor an orientation or a combination of a location and orientation.

Then, the spatial position of each tool is measured. In order to fullyreflect the orientation and location of the wire portion being held bythe tool, it is important that the bearings holding the tools aredesigned for extra low friction. Also, no relevant external forces mustbe acting onto the tools. Forces like gravity must be compensated byusing for instance counter weights or springs. Now only the remainingforces in the wire will drive the location and orientation of the tools.The tools will move until the wire is in its relaxed situation. If theinternal damping properties of the wire material should be too low, itmay be desirable to use additional damping elements in order to calmoscillations.

In a preferred embodiment, the apparatus used for the method will be anapparatus also used to bend the wire. The tools will be identical to thetools used for holding the wire when performing the desired deformation.In this way, the actual wire shape can be measured directly after thebend has been applied. This shape can be compared to the nominal shapewith the help of a computer. In a preferred embodiment, the computercalculates corrective movements in order to eliminate remainingdeviations from the ideal shape. These movements are executed eithermanually by an operator that receives respective instructions from thecomputer, or the computer has direct control over actuators that arecoupled to the gimbal axes, and executes the necessary movementsautomatically. When the errors do not exceed predefined tolerances, thedeformation process is regarded as successful, and the gripper isreleased and the gimbal axes are reset.

The remaining deviation of an actual bend from the nominal value can beused for recalculating the subsequent bends. FIG. 16 displays a wire 68having a first bend 69. This bend deviates from the nominal bendrepresented by the nominal midline 67. FIG. 17 displays the wire afterthe second bend 70 has been applied. The distance between both bends hasbeen slightly shortened, and the angle has been increased. Thus theoriginal error in bend 69 has been compensated. Depending on thespecific configuration of bends, a full compensation as demonstrated inFIGS. 16 and 17 may not be possible, but a partial compensation cane beperformed. Again, the error in the second bend 70 will be measured, anda compensation of the determined deviation from the nominal value willbe performed on subsequent bends.

It is obvious that an apparatus as shown in FIG. 13 or 15 with agimbal-mounted moveable gripper is perfectly suited for measuring theactual shape of the wire. The moveable components of such an apparatuscan be perfectly balanced. Also, measuring the actual angles can beperformed by contact-free rotary encoders 50, 54 and 57. During themeasuring process the wire is held, but no forces are applied onto thewire. In a preferred embodiment, all actuators that are used to drivethe axes are completely decoupled from the axes.

The words used in this specification to describe the invention and itsvarious embodiments are to be understood not only in the sense of theircommonly defined meanings, but to include by special definition in thisspecification structure, material or acts beyond the scope of thecommonly defined meanings. Thus if an element can be understood in thecontext of this specification as including more than one meaning, thenits use in a claim must be understood as being generic to all possiblemeanings supported by the specification and by the word itself.

Insubstantial changes from the claimed subject matter as viewed by aperson with ordinary skill in the art, now known or later devised, areexpressly contemplated as being equivalent within the scope of theclaims. Therefore, obvious substitutions now or later known to one withordinary skill in the art are defined to be within the scope of thedefined elements.

It must be understood that the illustrated embodiment has been set forthonly for the purposes of example and that it should not be taken aslimiting the invention. It will be apparent to those skilled in the artthat alterations, other embodiments, improvements, details and uses canbe made consistent with the letter and spirit of the foregoingdisclosure and within the scope of this patent, which is limited only bythe following claims, construed in accordance with the patent law,including the doctrine of equivalents.

In the claims which follow, reference characters used to designate claimsteps are provided for convenience of description only, and are notintended to imply any particular order for performing the steps.

1. A method of bending an orthodontic wire performed by a bendingapparatus, comprising the steps of holding a first portion of the wirewith first holding means; holding a second portion of the wire withsecond holding means, the second portion of the wire substantiallylongitudinally spaced apart from the first portion of the wire; andperforming a relative movement between the first holding means and thesecond holding means along at least one axis so as to place a bend inthe wire having a desired configuration, the first holding meansallowing substantially unrestricted longitudinal movement of the firstportion of the wire at least during the process of actually deformingthe wire such that the wire is pulled through the first holding means.2. A method as defined in claim 1, further comprising the step ofperforming the relative movement between the first and the secondholding means so as to extend the wire through the first holding means.3. A method as defined in claim 1, wherein the method steps areperformed repeatedly in a numerically controlled process so as to placeat least two bends in the wire.
 4. A method as defined in claim 1,wherein the relative movement is at least partially non-perpendicularrelative to the longitudinal axis of the first portion of the wire.
 5. Amethod of shaping a customized orthodontic wire and measuring the actualshape applied, comprising the steps of holding different portions of thewire by two separate and spaced apart holding means, the holding meansbeing moveable relatively to each other, performing a relative movementbetween the two holding means by means of at least one numericallycontrolled actuator so as to reshape the wire to a desiredconfiguration; substantially isolating at least one of the two holdingmeans from forces imposed by the at least one numerically controlledactuator; and measuring the relative position between the two holdingmeans.
 6. A method of shaping an orthodontic wire and measuring theactual shape applied, comprising the steps of holding different portionsof the wire by two separate and spaced apart holding means, the holdingmeans being moveable relatively to each other; performing a relativemovement between the two holding means by means of at least onenumerically controlled actuator so as to reshape the wire to a desiredconfiguration; compensating at least partially for forces acting onto atleast one of the two holding means with the exception of forces imposedby the wire; and measuring the relative position between the two holdingmeans.
 7. An apparatus for shaping an orthodontic wire, comprising atleast first and second holding means to shape a bend into the wire, thefirst and the second holding means each separately holding and grippingthe wire at a substantially different longitudinal position of the wire,at least one of the first and second holding means allowing asubstantially unrestricted longitudinal movement of the wire at leastduring the process of actually deforming the wire, and at least one ofthe holding means mounted onto a movable axis.
 8. An apparatus asdefined in claim 7, further comprising means for numerically controllingthe position of at least one of the axes.
 9. An apparatus as defined inclaim 7, further comprising means for substantially isolating at leastone of the axis from forces other than imposed by the wire.
 10. Anapparatus as defined in claim 7, further comprising means forsubstantially compensating forces acting onto at least one of the axeswith the exception of forces imposed by the wire.
 11. An apparatus asdefined in claim 7, further comprising means for measuring the positionof at least one of the axes.
 12. An apparatus as defined in claim 7,wherein at least one of the holding means is gimbal mounted and moveablein at least two axes.
 13. An apparatus as defined in claim 7, whereintwo of the holding means are mounted each onto a pivoting axis allowinga rotational movement, the pivoting axes of said movements beingsubstantially equal to the longitudinal axes of portions of the wirebeing held by the holding means, and wherein at least one of thepivoting axes is mounted onto another rotational axis beingsubstantially perpendicular to both of the pivoting axes.
 14. Anapparatus as defined in claim 7, wherein the first holding means guidesthe wire and the second holding means grips the wire during the processof actually deforming the wire.
 15. An apparatus as defined in claim 7,wherein the substantially unrestricted longitudinal movement of the wireis substantially unrestricted unidirectional longitudinal movementwithin the holding means.
 16. An apparatus as defined in claim 7,wherein the at least one of the holding means mounted onto a movableaxis performs at least partially a non-perpendicular movement relativeto the longitudinal axis of a portion of the wire held by the firstholding means.
 17. An apparatus for bending an orthodontic wire,comprising: at least two holding means for placing a bend into the wire,at least one of the holding means allowing substantially unrestrictedlongitudinal movement of the wire at least during the process ofactually deforming the wire, and at least one of the holding meansmounted onto a moveable axis; and means for numerically controlling theposition of at least one of the axes.
 18. An apparatus for bending anorthodontic wire, comprising: at least two holding means for placing abend into the wire, at least one of the holding means allowingsubstantially unrestricted longitudinal movement of the wire at leastduring the process of actually deforming the wire, and at least one ofthe holding means mounted onto a movable axis; and means forsubstantially isolating at least one of the axis from forces other thanimposed by the wire.
 19. An apparatus for bending an orthodontic wire,comprising: at least two holding means for placing a bend into the wire,at least one of the holding means allowing substantially unrestrictedlongitudinal movement of the wire at least during the process ofactually deforming the wire, and at least one of the holding meansmounted onto a movable axis; and means for substantially isolating atleast one of the axis from forces other than imposed by the wire.
 20. Anapparatus for bending an orthodontic wire, comprising: at least twoholding means for placing a bend into the wire, at least one of theholding means allowing substantially unrestricted longitudinal movementof the wire at least during the process of actually deforming the wire,and at least one of the holding means mounted onto a movable axis; andmeans for measuring the position of at least one of the axes.
 21. Anapparatus for bending an orthodontic wire, comprising at least twoholding means for placing a bend into the wire, at least one of theholding means allowing substantially unrestricted longitudinal movementof the wire at least during the process of actually deforming the wire,and at least one of the holding means mounted onto a movable axis, andat least one of the holding means is gimbal mounted and moveable in atleast one of the axes.
 22. An apparatus for bending an orthodontic wire,comprising at least two holding means capable of placing a bend into thewire, at least one of the holding means allowing a substantiallyunrestricted longitudinal movement of the wire at least during theprocess of actually deforming the wire, two of the holding means eachbeing mounted onto a pivoting axis allowing a rotational movement, thepivoting axes of said movements being substantially equal to thelongitudinal axes of portions fo the wire being held by the holdingmeans, at least one of the pivoting axes mounted onto another rotationalaxis being substantially perpendicular to both of the pivoting axes.